I. Field of the Invention
The invention relates to severing and sealing tools for cutting and sealing thermoplastic material, and, more particularly, this invention relates to cutting and sealing tools for thermoplastic material which have two electrical resistive wires, one wire for severing the thermoplastic material which is under tension and the other sealing the layers of thermoplastic material together.
II. Description of the Prior Art
Reference is made to the following U.S. Patents: U.S. Pat. No. 3,245,294 issued to Butler et al on Apr. 12, 1966 and entitled "Means For and Method of Cutting Thermal Plastic Materials;" and U.S. Pat. No. 3,064,111 issued to Newman on Nov. 13, 1962 and entitled "Plastic Cutting Device."
The Butler Patent shows a heated tip which is utilized to cut a thermoplastic material by applying heat to the tip to bring the tip to the softening temperature of the thermoplastic material. After the cutting operation, an impulse of heat is applied to the tip to heat it above the decomposition temperature of the material to clean the tool. The Butler patent is particulary adaptable to cutting a thermoplastic material which is disposed between two rigid structures (as shown in FIG. 4 of the patent).
The Newman patent is of more interest because it shows the utilization of electrically resistive wires through which current is passed in order to heat the wires for cutting a thermoplastic material. In the Newman patent, the cutting wire is moved basically perpendicular to the thermoplastic material during the cutting operation and the electrically resistive wire is heated to a temperature which is within the softening range of the thermoplastic material. The cutting of the thermoplastic material is accomplished by softening the plastic material by the use of heat and severing the material by the sawing action of the thin wire through the material.
It is known to cut plastic through the use of heated blades or wires. It is also known to seal plastic strips together by utilizing friction heat to melt or fuse the overlapping portion of the strap, i.e., the overwrapped or two-layer portion of the strap, together. Sufficient heat is applied to the strap by means of friction in U.S. Pat. No. 3,654,033 issued to Angarola on Apr. 4, 1972 and entitled "Strap Tensioning and Sealing Tool"to accomplish the sealing operation. The Angarola patent further shows cutting of the portion of the strap between the overlapping portion and the supply somewhere adjacent to the overlapping portion prior to the sealing of the strap. The Angarola patent further shows placing the strap in tension around the object to be wrapped by placing tension on the portion of the strap toward the strap supply.
Other patents, which are of some interest, known to the applicants are, U.S. Pat. No. 3,985,996 issued to Fischer on Oct. 12, 1976 and entitled "Thermal Cutting Apparatus," U.S. Pat. No. 3,892,024 issued to VanZyl on Jul. 1, 1975 and entitled "Articles of Cutlery, Paint Scrapper and the Like," U.S. Pat. No. 4,014,229 issued to Lynch on Mar. 29, 1977 and entitled "Film Dispenser and Cut Off," U.S. Pat. No. 4,018,117 issued to Patterson on Apr. 19, 1977 and entitled "Cutting Method and Machine Employing Heated Reciprocating Wire," U.S. Pat. No. 2,987,598 issued to Chance et al on Jun. 6, 1961 and entitled "Devices for Severing Plastic Material," U.S. Pat. No. 2,711,779 issued to Carlan on June 28, 1955 and entitled "Method and Apparatus for Severing and Joining Layers of Thermal Plastic Material," U.S. Pat. No. 3,035,631 issued to Knowles on May 22, 1962 and entitled "Heating Tip for Welding of Plastics," U.S. Pat. No. 2,477,040 issued to Brown et al on July 26, 1949 and entitled "Sewing Machine for Thermal Plastic Materials," and U.S. Pat. No. Re.21070 issued to Raffles on May 2, 1939 and entitled "Heating Element".
None of the prior constructions known in the art shows a heating tool adapted for cutting and sealing thermoplastic material, which is overlapping and which is also under tension, by utilizing electrically resistive wires disposed across a single tool head with both of the electrically resistive wires being heated to the softening temperature of the thermoplastic material.